TAF1, the Largest Subunit of Tfiid, Is Dispensable for Adult Hematopoiesis

Temporal and spatial control of gene expression is central to normal hematopoietic stem cell (HSC) biology. Many sequence-specific transcription factors have been identified as key regulators of HSC fate decision, while the function of general transcription factors in HSC behavior is poorly understood. We previously reported that TAF1, the largest subunit of the TFIID complex, plays a critical role in AML1-ETO driven acute myeloid leukemogenesis. To evaluate the function of TAF1 in normal fetal and adult hematopoiesis, we generated TAF1 conditional knockout (CKO) mice and identified an essential role of TAF1 in fetal erythropoiesis. Surprisingly, deletion of TAF1 in adult mice was not lethal to hematopoiesis; rather, we observed a marked expansion of hematopoietic stem and progenitor cell (HSPC) populations, with increased self-renewal and impaired differentiation capacity in these TAF1- null cells. Consistently, we found that TAF1-null HSPCs failed to up-regulate key differentiation-associated genes when induced to differentiate in vitro. Using a variety of genome-wide assays and biochemical approaches, we found that TAF1 loss not only disrupted TFIID complex formation and chromatin recruitment, but also reduced promoter accessibility, impaired RNA Polymerase II promoter recruitment and activity, as well as its promoter-proximal pausing mechanism. Thus, the effect of TAF1 loss on normal adult hematopoiesis primarily relates to the inability to upregulate genes involved in differentiation, while HSC self-renewal and the expression of self-renewal genes proceeds relatively normally.

基因表达的时空控制对正常造血干细胞（HSC）生物学至关重要。许多序列特异性转录因子已被确定为HSC命运决定的关键调节因子，而通用转录因子在HSC行为中的作用却鲜为人知。我们先前报道，TAF1（TFIID复合物的最大亚基）在AML1 - ETO驱动的急性髓系白血病发生中起关键作用。为了评估TAF1在正常胎儿和成人造血中的功能，我们构建了TAF1条件性敲除（CKO）小鼠，并确定了TAF1在胎儿红细胞生成中的重要作用。令人惊讶的是，在成年小鼠中敲除TAF1对造血并非致命；相反，我们观察到造血干细胞和祖细胞（HSPC）群体显著扩增，这些TAF1缺失细胞的自我更新能力增强且分化能力受损。一致地，我们发现当在体外诱导分化时，TAF1缺失的HSPC无法上调关键的分化相关基因。通过使用多种全基因组分析和生化方法，我们发现TAF1缺失不仅破坏了TFIID复合物的形成和染色质募集，还降低了启动子可及性，损害了RNA聚合酶II启动子的募集和活性以及其启动子近端暂停机制。因此，TAF1缺失对正常成人造血的影响主要与无法上调参与分化的基因有关，而HSC自我更新和自我更新基因的表达相对正常进行。